Subscribe
WordPress developers often need to insert small pieces of code to get certain features running smoothly on a website. One of the most common ways to do this is by editing the theme’s functions.php file.
If you’re just getting started with WordPress, the idea of tweaking theme files can feel intimidating. And honestly, even with experience, that feeling never fully disappears. But you can make the process much safer by choosing the right way to modify the functions.php file on your site.
Before we jump into the practical steps, let’s take a moment to understand what the functions.php file actually does. After that, we’ll walk through how to edit functions.php in WordPress and what you should keep in mind to avoid unexpected issues.
What is the functions.php File?
Every WordPress theme comes with its own functions.php file. Think of it as a collection of instructions — bits of code that define functions your website can use whenever they’re needed elsewhere in the theme.
In simple terms, this file holds the “action code” that other parts of your site rely on. Depending on the theme, your functions.php file might turn certain post types into blog pages, integrate Google Analytics, or include custom features that give your theme its distinct look and behavior.
For clarity, the file usually sits in:/wp-content/themes/your-theme/functions.php
And for child themes:/wp-content/themes/your-child-theme/functions.php
Understanding where it lives makes it easier to avoid editing the wrong file — especially if you have multiple themes installed.
Read also: Top 10 Mistakes to Avoid When Building a New Website on WordPress
Reasons to Be Cautious When Editing functions.php
Before you start making changes to your functions.php file, it’s important to understand a few key points:
- Changes apply only to the active theme: every theme has its own version of the functions.php file.
- Updates can erase your edits: when a theme is updated or reinstalled, your custom code may be overwritten.
- Mistakes can break your site: even a small typo in the functions.php file can lock you out of the dashboard or trigger unexpected errors.
Because this file plays such a critical role in how your website functions, modifying it always comes with some level of risk. A broken functions.php file can take your entire site down, so having a clear path to undo your last changes is essential — especially for eCommerce or high-traffic websites.
To minimize downtime and avoid headaches, make sure you:
- Test your changes on a staging environment
- Create a backup of the file before editing
- Make one change at a time so you can easily revert if needed
- Only edit the file when it’s really necessary — usually within a child theme
- Consider using a site-specific plugin to handle individual code snippets instead
If you’re troubleshooting other issues, feel free to check out our article on WordPress Problems Solved, where we walk through common WordPress challenges and how developers of all levels can fix them.
How to Use a Plugin Instead of Editing functions.php Directly (Safest Method)
If you want to add custom functionality to your WordPress site without risking theme-related issues, the simplest and safest route is to use a plugin rather than editing the functions.php file manually. Tools like Code Snippets let you insert and manage small pieces of code in an isolated environment.
Because these plugins operate independently from your theme, your custom snippets won’t disappear when the theme is updated or replaced. This removes one of the biggest risks of editing theme files directly and gives you a far more stable way to maintain and test your changes over time.
For developers who need full control, WordPress also supports mu-plugins (must-use plugins). These are always active, load before regular plugins, and remain untouched by theme changes — a great option for functionality that must never be disabled.
How to Edit functions.php in WordPress Using the Admin Theme Editor
WordPress includes a built-in Theme Editor that allows you to view and adjust your theme’s files directly from the dashboard. Working with the functions.php file through this editor is fairly straightforward once you understand how WordPress handles source code changes inside the admin area.
Important: Avoid using this method on a live production site unless you have no other choice. A simple error in the functions.php file can instantly break your website, and if that happens, you won’t be able to reach the Theme Editor to fix it.
If you still have access to wp-admin, you can make modifications through the default WordPress interface:
- Sign in to your WordPress dashboard as an administrator.
- Go to Appearance → Theme Editor to open the file editor.
- Confirm that you’re editing the correct theme, or switch to another one using the Select theme dropdown.
- In the list under Theme Files, locate and click functions.php.
- Apply your changes, then click Update File to save them.
Keep in mind: every theme comes with its own separate functions.php file. Double-check that you’re editing the right theme; otherwise, your modifications may be saved in the wrong location and won’t appear on the site.
Read also: How to Disable WordPress Auto-Updates Safely
Accessing the functions.php File Through an FTP Client
Using an FTP (File Transfer Protocol) or SFTP (Secure File Transfer Protocol) client is another quick and reliable way to reach your website’s files. If you prefer working directly with your server’s directory instead of using the WordPress dashboard, an FTP/SFTP client gives you full access. There are plenty of programs available — both free and paid — so you can choose whichever tool you’re most comfortable with.
To open or replace your functions.php file through an FTP client, follow these steps:
- Connect to your website using your chosen FTP/SFTP client and the login details provided by your hosting service.
- Once connected, you’ll see two panels: one showing your local computer files and the other displaying your website’s server files. Navigate to the theme folder you want to edit, then locate the functions.php file.
Tip: You may need to check multiple directories depending on how your theme is structured. - Upload your updated functions.php file to the correct theme directory on your WordPress site.
Important: Allow the upload to finish completely before disconnecting. Interrupting the transfer — even briefly — can corrupt the file and potentially take your site offline.
If your site does break, enabling WordPress debug mode in wp-config.phpdefine('WP_DEBUG', true);
can help you quickly identify the error.
Use a Professional or Managed Services
Sometimes the smartest and most time-efficient choice is to pass technical tasks to someone who works with WordPress every day. There’s no downside to admitting that certain jobs go beyond your current skill level — or simply aren’t worth the hours you’d need to spend on them. If you’d rather stay focused on your business, a managed WordPress service provider can take the burden off your shoulders.
At CoDiCo, we offer a variety of WordPress care plans and maintenance packages designed to keep your website running smoothly. Whether you need help with backend changes, ongoing site management, or full technical support, our team handles the heavy lifting so you can focus on what matters most.
Read also: Boost Your WordPress Site Speed: A Simple Guide
Frequently Asked Questions
1. How can I safely edit the functions.php file in WordPress?
You can modify the functions.php file through the Theme Editor, via FTP/SFTP, or by using a code-snippet plugin. The safest approach is using a plugin, since it prevents errors from taking your site offline and keeps your changes intact during theme updates.
2. What’s the easiest way to access the functions.php file?
The simplest method is through the WordPress dashboard. Go to Appearance → Theme Editor, select the correct theme, and open the functions.php file from the list of theme files.
3. Can I add custom code to functions.php?
Yes, but do so carefully. You can paste your snippet into the functions.php file using the Theme Editor or FTP. If you prefer not to touch theme files, a snippet plugin lets you add code separately without risking theme-related issues.
4. Where can I find the functions.php file in my WordPress installation?
It’s located inside your active theme folder:/wp-content/themes/your-theme/functions.php
If you’re using a child theme, you’ll find it in the child theme’s directory instead.
5. What happens to my custom code if I switch or update themes?
Any custom code stored in functions.php belongs to the theme it’s added to. Updating or switching themes will remove those changes unless you reapply them to the new theme or keep them inside a plugin instead.
6. Does CoDiCo offer help with managing WordPress sites?
Yes. CoDiCo provides a wide range of WordPress services—from routine maintenance and security monitoring to performance optimization and backend support. If you prefer not to handle technical tasks yourself, our team can manage your site for you.
